Fuel cell system in the form of a printed circuit board

ABSTRACT

A planar fuel cell system comprising at least two fuel cells which are electrically connected in series in a plane via horizontally overlapping connecting lugs and comprise an anode current collector on the anode side and comprise a cathode current collector on the cathode side is provided. The current collectors are electrically connected to the connecting lugs and a polymer electrolyte membrane, wherein the current path is led around the polymer electrolyte membrane. The fuel cell system is designed with a printed circuit board technique and as a composite of a first, anode-side printed circuit board and a second, cathode-side printed circuit board, and the current collectors and connecting lugs are designed as strip conductors of these printed circuit boards. Methods of manufacturing the fuel cell system are also provided.

This application is the U.S. national phase of international patentapplication PCT/EP03/03772, filed on Apr. 11, 2003, and claims priorityto German patent application number 102 17 034.7, filed Apr. 11, 2002,all of which are hereby incorporated by reference.

The invention relates to a planar fuel cell system with which at leasttwo fuel cells are arranged in a plane and are electrically connected inseries via connecting lugs which overlap horizontally, wherein thecurrent path running the fuel cell system is led around the polymerelectrolyte membrane contained in the fuel cell system, so that themembrane is not penetrated. The invention further relates to a methodfor manufacturing such a fuel cell system.

BACKGROUND OF THE INVENTION

For the addition of the individual voltages of fuel cells and achievinga higher total voltage which this entails, it is known to connectseveral fuel cells electrically in series. Evidently then, for this,several fuel cells are connected together in a fuel cell system.

Usually for this, several fuel cells are arranged above one another andare pressed together by two end plates by way of screw connections(stack design). However, with regard to the geometry of the fuel cellsystem, a large constructional height and an unfavourable ratio of theedge length of the fuel cell system result on account of this design.

Since, for many applications, it is desirable to realise a fuel cellsystem with a significantly flatter geometry, there exists the need toconnect the fuel cells in a fuel cell system in series in a plane. Herethere are various ideas known from the state of the art:

The patent document DE 195 02 391 C1 and the PCT published applicationdocument WO 96/18217 disclose so-called “strip membrane fuel cells” withwhich the fuel cells are arranged next to one another and are connectedto one another in series. The series connection is realised here in amanner such that a traverse conducting structure connects the cathodeside of a fuel cell to the anode side of a further fuel cell and at thesame time penetrates through the membrane contained in the fuel cells.With this, there exists the disadvantage that leakages may easily occurdue to the passage of the transverse conductor through the membrane.

The U.S. Pat. No. 6,127,058 discloses a fuel cell system with which thefuel cells are arranged in a plane and are connected in series by way ofouter-lying connecting lugs. With this solution, although the currentpath does not penetrate the membrane, the technical manufacturingexpense is very active and prone to breakdown on account of the design,particularly with regard to the individual large-scale manufacture.Furthermore, it is considerably disadvantageous that at least two partsto be assembled individually as current dischargers are required foreach cell.

In S. J. C Cleghorn et al.: “A printed circuit board approach tomeasuring current distribution in a fuel cell”, Journal of AppliedElectrochemistry 28 (1998) 663-627, the idea of measuring the currentdistribution of a fuel cell by way of using a fuel cell whose currentcollector and gas distribution structure (flow field) on the anode sidehas been realised in a construction manner of a [printed] circuit boardand in a segmented manner is described. The construction described herehowever is only suitable for locally resolved diagnosis purposes in theexperimental field. Here too there is no series connection since forthese diagnosis and measurement purposes (current, voltage, impedancespectroscopy) only individual cell segments are tapped.

It is the object of the present invention to specify a fuel cell systemwhich has a low technical expense and may be manufactured economicallyin industrial large-scale manufacture, which is robust in its field ofapplication and may be applied in a manner which is particularlytechnically simple, which has a flat geometry and which delivers anincreased output voltage with respect to fuel cells contained in thefuel cell system. Furthermore, the disadvantages of the mentioned stateof the art are to be avoided.

It is further the object of the invention to specify a method formanufacturing such a fuel cell system.

This object preferbly is achieved by the characterizing features of thepresent invention.

BRIEF SUMMARY OF THE INVENTION

By way of the fact that the fuel cell system is constructed with[printed] circuit board techniques, one applies reliable seriesproduction manufacturing technology in order to economically manufacturea fuel cell system with a low electrical output in large-scalemanufacture. This relates also and in particular to the contactingbetween the fuel cells which are contained in the fuel cell system andare connected to one another in series, which are realised with triedand tested methods of [printed] circuit board technology.

By way of the fact that the fuel cell system is designed as a compositeof a first, anode-side printed circuit board and of a second,cathode-side printed circuit board, on the one hand the number ofdifferent components which are to be produced during manufacture of sucha system is reduced and thus the manufacturing is simplified, and on theother hand it is rendered possible to construct electronic circuits onthe printed circuit board composite. These may possibly obtain theenergy for the operation of the circuit from the fuel cell systemitself.

According to the character of the realisation of the fuel cell systemaccording to the invention in printed circuit board technology, currentcollectors which are required for the electron transport in the fuelcell, and connecting lugs via which the fuel cells contained in the fuelcell systems are connected to one another in series in a plane, arerealised as strip conductors of the printed circuit boards from whichthe printed circuit board composite is constructed.

Within the context of this application, a printed circuit board inprinted circuit board technology indicates a board, consisting of aprinted circuit board carrier (substrate) with a depositedmetallisation, wherein usually parts of the metallisation are removed,e.g. by way of an etching method or by way of milling, so that theremaining metallisation part forms an electrically conductive stripconductor. Such metallisations or strip conductors may be located on thefirst and/or second side of a printed circuit board.

By way of the fact that current collectors as well as connecting lugsare designed as strip conductors, these are spatially integrated intothe fuel cell system in a mechanically robust and furthermorespace-saving manner. Furthermore it is also advantageously renderedpossible to permit the current collector to merge into the connectinglugs in a smooth manner by way of using the same metallisation layer forrealising the respective strip conductor.

Advantageous embodiments and further developments of the solution willbe apparent from the description of the invention provided herein.

The fuel cell system may advantageously be developed further to theextent that the connecting lugs are located within the boundary of theprinted circuit board composite, thus the connecting lugs do not projectbeyond the outline of the printed circuit board composite. Themechanical robustness may thus be further improved and the expense withregard to technology may be reduced further with its practicalapplication and with the further processing.

If the fuel cell system is advantageously developed further to theextent that the horizontally overlapping connecting lugs in theiroverlapping region in each case are connected by way of at least onecontacting element, the connecting lugs are well defined with regard toone another and are brought into connection with one another in alasting manner and thus the electrical series connection is realised ina manner in accordance with printed circuit board construction. Thecontacting element is particularly advantageous when it is used incombination with the advantageous further development of the fuel cellsin each case having a reaction region incorporated into the printedcircuit-board, said reaction region being bordered by a raised part ofprinted circuit board material and/or lacquer, since then, on account ofthe perpendicular contacting elements, the arising vertical distancebetween the overlapping connecting lugs of two fuel cells contained inthe fuel cell system is bridged. The contacting element mayadvantageously be realised with a perpendicular design. It is howevernot limited to such a design.

A practical possibility for realising such a perpendicular contactingelement lies in designing it as a bore which is completely or partlyfilled with an electrically conductive material, for example with solderor electrically conductive adhesive.

One advantageous further embodiment lies in additionally leading anelectrically conductive linear element (wire, nail or bolt) through thebore, wherein the electrical contact between the connecting lug and theconductive, linear element is realised by way of conductive materialfilled into the intermediate space lying therebetween.

The bore on its inner side may be advantageously metallised, by whichmeans the contacting is further improved, and the liquid solder,encouraged by the capillary forces, may flow into the bore. This maypreferably be realised by way of a galvanically grown metal layer,wherein copper is preferably used.

It is also possible to design the perpendicular contacting elementwithout filling with electrically conductive material and only with themetallisation of the inner side of the bore.

It is further advantageous to provide several contactings for eachconnection of two overlapping connecting lugs, by which means therespective transition resistance is reduced further. An alternative,advantageous perpendicular contacting element is a rivet or press pinwhich additionally also contributes to the mechanical strength withrespect to the cohesion of the composite of the printed circuit boards.

The contacting element, given connecting lugs lying directly on oneanother, or given an only small distance between these, may be realisedby way of point welding (laser or resistance welding), wherein the stripconductor at least of one side (cathode-side or anode-side) must beaccessible from the outside for the welding.

A further realisation possibility of the contacting element lies indoing without the bores and filling the intermediate region of theoverlapping connecting lugs with a conductive adhesive or conductivelacquer. One advantageous further design of this embodiment lies inincorporating a sheet metal piece or a metal foil in the intermediateregion of the connecting lugs which the conductive adhesive surrounds.

Advantageously, gas distributor structures may be incorporated into thefirst anode-side printed circuit board and into the second cathode-sideprinted circuit board, wherein the second, cathode-side printed circuitboard additionally or in place of the gas distributor structures maycomprise air openings to the outside of the fuel cell system.

If the fuel cells of the fuel cell system in each case comprise areaction region incorporated into the printed circuit board, which isbordered by a raised part of printed circuit board material and/orlacquer defining the reaction region, then a pocket arises on account ofthis which defines the reaction region and furthermore renders possiblean improved fixation and an improved assembly of the diffusion layer inthe reaction region, as is provided for in a further advantageousembodiment.

In this further advantageous embodiment, in the reaction region in whicha diffusion layer is provided, there is also contained a gas distributorstructure and a current collector, and the diffusion layer is depositedonto the current collector in a flat manner. The diffusion layer at thesame time may be electrically contacted with the metal layer of thecurrent collector by way of soldering or an electrically conductiveadhesive, and may also be mechanically fastened.

The raised part of printed circuit board material and/or lacquer may ina practically particularly advantageous form be an interconnected framestructure, wherein the applied material may be plastic, FR4, impregnatedpaper or similar material which are laminated on or bonded on, epoxyadhesive which is printed on, or furthermore solder blocking lacquer.

The diffusion layer may be a carbon fibre paper or may be designed in aparticularly advantageous manner as a metallised plastic fabric, andspecifically in a manner such that it is the case of a plastic fabricwhich preferably only in the region of the electrodes has metallisedsegments, e.g. gold (nickel-gold). Suitable plastic fabrics of polyamideor nylon with diameters of the threads in the region of 20 and 100 μmand mesh widths of 30 to 500 μm are used as screen-printing fabric. Ametallic segmentation may at the same time be achieved by way of priormasking or photolithography of the plastic fabric.

For avoiding corrosion, it is advantageous to provide the stripconductors consisting for example of copper with single-ply ormulti-ply, electrically conductive and resistant coatings, such asnickel-gold, Cr or TiW.

The strip conductors, as also the remaining metallisations, within theframework of the whole invention, may consist of copper, nickel, to goldor stainless steel and/or alloys thereof.

For separating off the anode side from the cathode side in each case ofone reaction space which is realised by a first, anode-side and ananalogously constructed second, cathode-side printed circuit board, forthe composite of the two printed circuit boards, a proton-conductivepolymer membrane is applied between these printed circuit boards whichonly has catalytically coated segments in the region of the reactionspaces of the fuel cells in the fuel cell system. At the same time,preferably a segmented membrane electrode assembly (MEA) is used. Withthis, this membrane is not penetrated by the current path, i.e. by thestrip-conductor-like current collectors and connecting lugs or by theperpendicular connection elements which connect the horizontallyoverlapping connecting lugs of two fuel cells.

Hereinafter the advantages of the invention with regard to themanufacturing method of a fuel cell system according to the inventionare described:

By way of the fact that a first and a second printed circuit boardcarrier (substrate) in each case is selected with an upper side and alower side and for both carriers (substrates) a number of equal methodsteps is carried out in each case on the upper side, one may reduce theexpense for manufacture with industrial large-scale production. This isaccomplished by way of manufacturing several fuel cell systems from asinge printed circuit board (multiple use).

By way of the fact that the printed circuit board carrier (substrate) ineach case is provided with a metallisation so that a printed circuitboard within the context of the present invention arises, and by way ofthe fact that this metallisation is selectively etched away in partregions of the printed circuit board so that strip conductors arise, ina reliable manner capable of series production, current collectorsrealised as a strip conductors and likewise strip-conductor-likeconnecting lugs which are contiguous with these in a smooth manner areproduced in the reaction spaces.

The connecting lugs at the same time do not necessarily have to be inthe same plane as the current collectors, but may also be realised as afurther strip conductor in the form of a metallisation on the lower sideof the strip conductor.

By way of the fact that gas distributor structures are incorporated intothe printed circuit board, the reactands are led to the reaction spaceand distributed here. The incorporation may for example be effected byway of milling, wherein in the case of a thin strip conductor in thereaction region (for example about 30 μm to 100 μm) one mills throughthe plane of the strip conductor in the direction of the printed circuitboard lower side, and in the case of a thick conductor layer (e.g. 200μm to 500 μm) one mills or etches into the strip conductor layer itself.

By way of the fact that a raised part surrounding the reaction spaces isdeposited, a recess arises in each case in the region of the reactionspaces, by which means advantageously the assembly of the diffusionlayers is simplified. With this assembly, an electrical and mechanicalconnection to the strip conductor plane and the diffusion layer may beeffected by way of soldering or a conductive adhesive. The assembly mayalso be encouraged only by way of a pointwise mechanical connection byway of a non-conductive adhesive.

Firstly a first, and a second intermediate product arise in this manner.

By way of the fact that subsequently the membrane electrode assembly(MEA) is deposited onto the upper side of the first intermediate productand that the first and the second intermediate product are joinedtogether with their upper sides facing one another, by way of the MEA,separated anode-side and cathode-side reaction spaces arise. The joiningmay be realised by way of screwing the two plates to one another outsidethe reaction regions, and/or bonding then to one another under pressure,by which means the contact resistance between the strip conductor andthe diffusion layer as well as between the diffusion layer and themembrane electrode unit is reduced.

By way of the fact that the connecting lugs of the anode-side andcathode-side printed circuit board are connected to one another, theelectrical series connection of the fuel cells contained in the fuelcell system is created.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is explained hereinafter by way of severalembodiment examples with figures. There are shown in

FIG. 1 the schematic construction of a fuel cell with printed circuitboard technology, in a cross section, which according to the inventionis designed as a composite of two printed circuit boards,

FIG. 2 the schematic construction of the anode-side printed circuitboard, in a plan view,

FIG. 3 the schematic cross section in the region of the reaction spaceand of the MEA of a first embodiment form of a fuel cell systemaccording to the invention, with three fuel cells, which are connectedin series in a plane,

FIG. 4 the schematic cross section in the region outside the membraneelectrode assembly (MEA) through a first embodiment of a fuel cellsystem according to the invention, with three fuel cells, which areconnected in series in a plane,

FIG. 5 the schematic upper and lower view of one of the two printedcircuit boards shown in FIG. 4, of the printed circuit board composite,without a deposited raised part, diffusion layer and MEA.

FIG. 6 the schematic cross section of a second embodiment form of thefuel cell system according to the invention, with which three fuel cellsin the printed circuit board composite are not only connectedelectrically in series in a plane via inner-lying connecting lugs, butalso via strip conductors on the surface of the printed circuit boardcomposite,

FIG. 7 the view of the upper and lower side of one of the two printedcircuit boards of the printed circuit board composite in FIG. 6 withoutthe deposited raised part, diffusion layer and without MEA,

FIG. 8 the schematic cross section of a third embodiment form of thefuel cell system according to the invention, with which in the printedcircuit board composite three fuel cells are connected electrically inseries in a plane not only by way of inner lying connecting lugs, butalso via strip conductors which are on the reaction region side andwhich face one another, on the respective sides, which face one another,of the anode-side and cathode-side printed circuit board, and which arewelded from an opening accessible to the outside,

FIG. 9 the view of the upper and lower side of one of the two printedcircuit boards of the printed circuit board composite in FIG. 8, withoutdiffusion layer and MEA, but with a deposited raised part,

FIG. 10 the schematic cross section in the region of the reaction spaceof a fourth, alternative embodiment of the fuel cell system according tothe invention, with four fuel cells whose anodes and cathodes arearranged alternately on an upper and lower printed circuit board, andare connected in series in a plane by way of connection of the currentcollectors of two adjacent anodes and cathodes by way of a stripconductor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic cross section through a fuel cell with printedcircuit board technology, which is designed as a composite of a first,anode-side printed circuit board 10 and a second cathode-side printedcircuit board 11. The two oppositely lying printed circuit boards 10 and11, which in this case are constructed in completely equal manner andare deposited onto one another rotated by 180° to one another about thespatial vertical, in their reaction region are separated by the membraneelectrode assembly (MEA) 3 and are connected to one another at theedges. The common reaction region formed by the two printed circuitboards 10 and 11 of the printed circuit board composite at the same timeconsist of the gas distributor structures 6, the current-collectors 1and the diffusion layers 2 of both printed circuit boards as well as ofthe previously mentioned MEA 2 with the porous catalytic coating 4.

As may be deduced from the Figure, the gas distributor structures 6 areincorporated into the printed circuit boards 10 and 11 by way of thefact that in each case the upper-lying copper strip conductor formingthe current collector 1 has been penetrated. Alternatively, with thickcopper strip conductors of about 200 μm to 500 μm it is possible toincorporate the gas distribution structures into the copper stripconductor itself. By way of this arrangement of the gas distributorstructures, the side of the gas distributor structures which faces theMEA 3 terminals with the plane of the current collectors 1 in a flushmanner. The diffusion layer 2 is deposited onto this plane over the areaso that the reactands supplied via the distribution structure 6 mayenter into the diffusion layer 2, and so that the diffusion layer 2 isalso electrically connected to the current collectors 1.

The diffusion layer may at the same time consist of carbon-fibre paper,preferably however also may be designed as a plastic fabric 2′ which inthe region of the current collector 1 metallised segments (e.g. gold,nickel gold); Suitable plastic fabric of polyamide or nylon withdiameters of the threads in the region between 20 μm and 100 μm and meshwidths of between 30 μm and 500 μm are used as screen printing fabric.Although methods for the permanent metallisation of such fine plasticfabrics are known, the segment structure may be achieved by way of amasking or photolithography of the plastic fabric which precede themetallisation.

In this example, advantageously the diffusion layer 2 is electricallycontacted and also mechanically fastened to the current collector 1 byway of soldering or electrically conductive adhesive. In order to betterfix the diffusion layers and to simplify the assembly of the diffusionlayer, the diffusion layers may be surrounded by a raised part 13 ofprinted circuit board material, so that in each case a recess (pocket)arises in the part of the printed circuit boards 10 and 11 which formsthe reaction space, and thus a frame structure is formed. This framestructure is characterised by the distance of the bonding joint 7 to theplane of the current collector 1 and by nature is located outside thereaction region. This frame structure may be realised by way oflaminating-on or bonding-on plastic, FR4, impregnated paper or similarmaterial, by way of printing-on epoxy adhesive, solder-blocking lacqueror similar means.

The strip conductors in all present embodiment examples are manufacturedof copper or the other previously mentioned materials and within thereaction space of the respective fuel cell, thus where the stripconductors contact the diffusion layer, serve as current collectors.Outside the reaction spaces, the strip conductors are used fordischarging the current as well as for contacting the current dischargecontact 5 to the outside of the fuel cell system, as well as for formingconnecting lugs, i.e. for the electrical series connection of fuel cellsin the system. To avoid corrosion, the copper strip conductor is to beprovided with a single-ply (single-layer) or multi-ply (multi-layer)resistant coating (e.g. nickel-gold, Cr, TiW).

The contacts 5 and 5′ serve for the external electrical connection ofthe fuel cell system and are electrically bonded to the currentcollectors 1. Commercially available and standardised clamp contacts,connecting lugs, pins, rivets etc. may be used as outer contacts 5 and5′. In FIG. 1, the attachment of a lateral outer contact 5 andalternatively to this, the attachment of a perpendicular outer contact5′ to the outer side of the printed circuit board is represented, whichare connected to the strip conductor by way of soldering or riveting.

In the case of the use of methanol as a reactant, the outer side of theanode-side gas distributor is completely or partly manufactured of a gaspermeable membrane or a microstructure with microscopic openings, whichpermits carbon-dioxide gas bubbles to be transported out of the reactionspace by way of the microstructure or to be withdrawn to the outsidethrough the microscopic openings of the microstructure.

FIG. 2 shows the anode-side printed circuit board 10 of the fuel cellsystem of FIG. 1 in a plan view. Recesses of the gas distributionstructure 6 are incorporated into the plane of the current collector 1and the printed circuit board material lying thereunder. The membraneelectrode assembly is not drawn in this representation, but its positionin indicated by the dashed line 3′. In the present embodiment, the gasdistribution structure has a meandering course. The mechanicallydeposited raised part 13 forming a frame structure and surrounding thereaction space covers the current collector 1 in the edge regions. Forthis reason the current collector 1 in the plan view may only berecognized in the region of the reaction space. The current collector 1covered by the frame structure is laterally connected to the currentdischarge contact 5.

FIG. 3 shows a fuel cell system with printed circuit board technologywhich as a composite of an anode-side printed circuit board 10 and acathode-side printed circuit board 11 is basically constructedanalogously to the example shown in FIG. 1. Here three fuel cells areshown in a plane which are connected electrically in series outside theregion of the membrane electrode unit (MEA) but within the printedcircuit board composite.

Since this figure shows a cross section within the region of thereaction space, the series connection is not shown in more detail here.

The proton-conductive polymer membrane 3 is preferably designed as asegmented MEA 3″ which is segmented in a manner such that the MEA 3″only has catalytically coated segments 4 in the region of the reactionspaces of the fuel cell system. The segmentation may at the same time beadvantageously incorporated into an MEA which has been catalyticallycoated over the whole surface, such as by way of laser ablation orreactive ion etching (RIE).

Instead of a cathode-side gas distribution structure, the embodimentexample has air openings 9 to the outside of the printed circuit boardcomposite. The printed circuit boards 10 and 11 are screwed to oneanother or bonded under pressure, to reduce the contact resistance atthe edge. Connection joints 7 arise.

The raised parts 13 forming the frame structure here, as also in theother embodiment examples, circumscribe the reaction regions.

FIG. 4 shows a schematic cross section outside the MEA through a fuelcell system of three fuel cells, with printed circuit board technology.Here a preferred way of electrically connecting the fuel cells in seriesin a plane outside the region of the MEA is represented.

This is effected in that the copper strip conductor of the currentcollector 1 is led into the outside of the reaction region butpermanently in the inside of the boundary of the printed circuit boardcomposite. Thus the connecting lug 8′ of the printed circuit board 11arises. The copper strip conductor of the fuel cell in the middle inFIG. 3 is likewise led outwards whilst forming the connecting lug 8. Theconnecting lugs 8 and 8′ lie opposite one another in the verticaldirection, thus overlap in a horizontal manner. At the same time theconnecting lugs 8 and 8′ are connected by way of perpendicularcontacting elements 12 for creating the electrical contact.

In order not to penetrate the membrane electrode assembly (MEA) 3, thestrip conductor of the current collector 1 is led in the region outsidethe polymer membrane or MEA 3 in the form of a connecting lug 8, intothe intermediate space of two adjacent fuel cell assemblies. A bore 12is formed through the printed circuit board composite for contacting theoppositely lying strip conductor lugs 8, 8′.

The conductive connection in the form of contacting elements 12 betweenthe connecting lugs 8 and 8′ arise on account of meting the inner sideof the bore 12. This is preferably realised by way of a galvanicallygrown copper layer. In order to further improve the contacting, the boremaybe completely or partly filled with solder or conductive adhesive.The contacting may also be realised without the inner-side metallisationof the bore only by way of the complete or partial filling of the borewith solder or conductive adhesive.

The contacting by way of a contact element 12 in the form of anelectrically conductively filled bore may be advantageously varied tothe extent that before joining together the printed circuit boards 10and 11, on the reaction-space side, one drills in each case a bore witha larger diameter so that a larger surface of the connecting lugs 8 and8′ is released. Then, by way of a bore of a smaller diameter one createsa continuous bore from the opposite side, wherein the thinner bore liescoaxially in the thicker bore and the thinner bore penetrates theconnecting lugs 8 and 8′. By way of filling with solder or conductiveadhesive, then, as previously described, the contacting of the twoconnecting lugs 8 and 8′ to one another may be carried out. On accountof the thicker, first bore, as a whole a larger surface of theconnecting lugs facing one another is released and thus an improvedelectrical contacting is achieved.

The particular preference of this type of contacting by way ofhorizontally overlapping connecting lugs 8 and 8′ and perpendicularcontacting elements 12 lies in not penetrating the proton-conductivepolymer membrane 3 which in each case on the anode side and cathode sideseparates the reaction spaces from one another.

If the contacting element 12 instead of a filled bore is realised by arivet or press pins, then simultaneously for the electrical contactingthe pressing pressure of the printed circuit board composite is alsorealised. Furthermore, this possibility has a very low contactresistance and no temperature loading on assembly. If the printedcircuit board material is removed between a connecting lug 8 and thesurface of a printed circuit board 10 or 11 on the reaction region side,then a welding connection is also possible. For connecting the printedcircuit boards 10 and 11, a clamping connection is alternatively oradditionally conceivable.

FIG. 5 shows the plan view of the surface of the printed circuit board10, said surface lying on the reaction region side (II) and lying on theoutside (I) in the printed circuit board composite, without a depositedraised part, without diffusion layers 2 and without MEA 3, wherein theposition of the MEA is indicted by the dashed line 3′.

On the reaction region side (II), one may clearly recognise theserpentine structure of the gas distributor structures 6. The term “gasdistributor structures” within the context of this patent applicationindicates all distributor structures for distributing and supplying thereactands in and to the reaction region. At the same time, thedistributor structures or the reactands are not limited to those whichare gaseous. Other forms are just as conceivable, such as liquid ones,like methanol.

In the view (II) on the reaction region side, the strip conductor whichsurrounds the serpentine gas distribution structure and forms thecurrent collector 1 may be recognised. This strip conductor 1 mergessmoothly into the connecting lugs 8, in the drawing in each case on theright at the top and on the right at the bottom of the reaction regionwith the gas distribution structure 6 and the current collector 1. Thereaction region whose boundary in this figure is represented by therectangle formed by the gas distribution structure 6 and the currentcollector 1, lies in the pocket which circumscribes this reaction regionand which is formed by the raised part of printed circuit board materialwhich is not shown in more detail in this figure. The gas distributionstructure at the same time penetrates this raised part forming thepocket at the location where two fuel cells are connected to one anotherwith regard to the supply of reactands.

The perpendicular contacting elements 12 are also shown in the figure,from the view (I) lying at the outside as well as from a view from thereaction region side (11) wherein in the latter view the penetration ofthe perpendicular connection elements is represented by the connectinglugs 8.

It is to be clearly seen that the electrical circuiting by way of theconnecting lugs 8 takes place outside the reaction region but within theouter boundary of the printed circuit board 10. By way of this one notonly achieves the advantage that on account of the electricalcontacting, the MEA 3′ indicated only in its position in this figure isnot penetrated and by way of this leakages may not arise, but also theusually high electrical losses in a planar arrangement of seriesconnected fuel cells is avoided by way of the fact that the currentthrough the preferably used well-conducting copper strip conductorswhich are formed by the current collectors 1 and the connecting lugs 8is discharged to the edge.

The FIGS. 6 and 7 show a second embodiment. Here the inner-lyingconnecting lugs 14 and 14′ of the printed circuit boards 10 and 11 areshown similarly to that in FIGS. 4 and 5, but the inner-lying connectinglugs 14 and 14′ (see FIG. 7) only form an extension of the currentcollectors to the outer region and no longer have the lateral extensionbent at an angle, in the direction of the adjacent fuel cell of theconnecting lugs 8 and 8′ of FIGS. 4 and 5.

The particularity of this variant of the electrical circuiting of thefuel cells in series in a plane lies in the fact that by way ofinner-lying connecting lugs 14 and 14′, in each case at least oneelectrical connection 15 to the outer-lying contacts 40 is created,wherein the outer-lying strip conductors 40 are arranged suchthat—analogously to the connecting lugs 8 and 8′—the outer lyingcircuiting strip conductors 40 in each case of two fuel cells overlap asshown in FIG. 6 and are connected to one another by way of one or moreperpendicular contacting elements 16. The basic integral homogeneity ofthe inner-lying connecting lugs 14 and the outer lying strip conductorsfor circuiting 40 becomes particularly evident from FIG. 7. In thisembodiment form the inner-lying connecting lugs 14 as well as theouter-lying strip conductors 40 are electrically contacted for theseries connection, wherein the electrical connection is realised inprinciple in the same manner as in the FIGS. 4 and 5.

FIGS. 8 and 9 show a third embodiment form. Here the inner-lyingconnecting lugs 17 and 17′ of the printed circuit boards 10 and 11, ineach case by way of a perpendicular contacting element 19, areelectrically connected to the strip conductors 18 and 18′ of theanode-side and cathode-side printed circuit board, said strip conductorsfacing one another. The strip conductors 18 and 18′ which on thereaction region side face one another, thus lie opposite one another,only have a slight distance to one another or form a border surface. Byway of the bore, the inner-side strip conductors 18 and 18′ lyingopposite one another, at a location at which this strip conductors lieopposite one another, are accessible from the outside and may bepermanently electrically contacted by way of point welding or laserwelding.

FIG. 10 shows the cross section through the reaction space of a furtherembodiment, wherein anode gas distributor structures 24 and cathode gasdistributor structures 23 are arranged in an alternating manner on eachof the printed circuit boards 21 and 22, wherein the current collector1′ of the cathode gas distributor is electrically connected to theadjacent current collector 1 of the anode gas distributor via a stripconductor 25.

In this example, the cathode gas distribution structure 23 isrepresented with air openings to the outside of the fuel cell system.Instead of air openings, one may also use a closed gas distributionstructure 24 such as that of the anode gas distributor 24.

The particular preference of this embodiment lies in the fact that byway of the alternating arrangement of the anode-sides and cathode-sidesof the fuel cells, one may do without a contacting of the one side ontothe other side of the printed circuit board composite. The fuel cell inthe printed circuit board composite may thus be realised merely by wayof bringing the two printed circuit boards 21 and 22 onto one another,which is not so tricky with regard to design, and is inexpensive tomanufacture.

A fuel cell system according to the invention, with a height of 2 mm to3 mm has only a very low constructional height. Due to the flat geometryof such a fuel cell system it is particularly suitable for integrationinto the outer housing of an apparatus. In particular with theconstruction manner with a cathode which is open to the outside orcorresponding openings to the outside for the supply of air, one mayoperate such a fuel cell system in a self-breathing and passive mannerwithout having to convectively supply oxygen such as by way of aventilator.

With printed circuit board technology, it is possible to provide amanufacturing technique which is compatible with series production andis reliable for manufacturing fuel cell systems with a relative lowelectrical output in large batch numbers in an inexpensive andtechnically less complicated manner. In particular, the electricalseries connection, i.e. the contacting of fuel cell to fuel cell of thefuel cell system may be realised by way of a tried and tested industrialmethod.

It is furthermore very advantageous that due to the design as a printedcircuit board composite, electronic circuits may be constructed on thefuel cell system in a simpler manner. Such circuits on the one hand maydetect, control or improve the behaviour of the fuel cell system and onthe other hand however the consumer to be supplied may also be depositeddirectly onto the printed circuit board composite. As examples of thefirst mentioned electronic circuits the following are to be named:electronics for DC-DC conversion, electronics which may be equipped withsensors, for measuring and detecting operating parameters of individualfuel cells current, voltage, impedance, temperature etc.) electronicsfor controlling the flows of reactands (activation of microvalves ormicropumps), electronics for the protection of individual fuel cells byway of protective or bypass diodes, or electronics for bridgingindividual fuel cells which are no longer capable of functioning.

One example of a consumer to be supplied directly on the printed circuitboard in the form of a microelectronic circuit is e.g. a sensor which issupplied electrically in a direct manner by way of the fuel cell system.

1. A planar fuel cell system comprising at least two fuel cells whichare electrically connected in series in a plane via horizontallyoverlapping connecting lugs and comprise an anode current collector onthe anode side and comprise a cathode current collector on the cathodeside, the current collectors being electrically connected to theconnecting lugs, and a polymer electrolyte membrane, wherein the currentpath is led around the polymer electrolyte membrane, wherein the fuelcell system is designed with a printed circuit board technique and as acomposite of a first, anode-side printed circuit board and a second,cathode-side printed circuit board, and the current collectors andconnecting lugs are designed as strip conductors of these printedcircuit boards.
 2. A fuel cell system according to claim 1, wherein theconnecting lugs are located within the boundary of the printed circuitboard composite.
 3. A fuel cell system according to claim 1, wherein theconnecting lugs in their overlapping region in each case are connectedby way of at least one perpendicular contacting element.
 4. A fuel cellsystem according to claim 3, wherein at least one perpendicularcontacting element is a bore filled with an electrically conductivematerial.
 5. A fuel cell system according to claim 4, wherein theelectrically conductive material is solder or an electrically conductiveadhesive.
 6. A fuel cell system according to claim 4, wherein the boreis metallised on its inner side.
 7. A fuel cell system according toclaim 3, wherein at least one perpendicular contacting element is arivet.
 8. A fuel cell system according to claim 1, wherein gasdistribution structures are incorporated into the first, anode-sideprinted circuit board.
 9. A fuel cell system according to claim 1,wherein gas distribution structures are incorporated into the second,cathode-side printed circuit board.
 10. A fuel cell system according toclaim 1, wherein air openings to the outside are incorporated into thesecond, cathode-side printed circuit board.
 11. A fuel cell systemaccording to claim 1, wherein the fuel cells in each case have areaction region which is incorporated into the first and second printedcircuit boards and which is circumscribed by a raised part of printedcircuit board material and/or lacquer.
 12. A fuel cell system accordingto claim 1, wherein the reaction region contains a gas distributionstructure and one of the anode or cathode current collectors, and adiffusion layer is provided which is deposited onto one of the anode orcathode current collectors in a flat manner.
 13. A fuel cell systemaccording to claim 1, wherein the diffusion layer is designed as aplastic fabric provided with metallised segments.
 14. A fuel cell systemaccording to claim 1, wherein the strip conductors and/or outer contactscontained in the fuel cell system are coated with single-ply ormulti-ply electrically conductive layers to avoid corrosion.
 15. A fuelcell system according to claim 1, wherein the polymer electrolytemembrane is designed as a segmented membrane electrode assembly (MEA).16. A fuel cell system according to claim 1, wherein on the surface ofthe printed circuit board composite it comprises an electronic circuit.17. A fuel cell system according to claim 1, wherein the connecting lugsare arranged in each case on the reaction region side of the first andof the second printed circuit board and are electrically contacted in apermanent manner by way of a welding connection.
 18. A planar fuel cellsystem comprising at least two fuel cells which via strip conductors areelectrically connected in series in a plane and which comprise currentcollectors electrically connected to the connection elements, and apolymer electrolyte membrane, wherein the current path is led around thepolymer electrolyte membrane, wherein the fuel cell system is designedin a printed circuit board technique and as a composite of a firstprinted circuit board and a second printed circuit board, and thecurrent collectors and connection elements are designed as stripconductors of these printed circuit boards, wherein the printed circuitboards in each case comprise alternating anode and cathode gasdistribution structures and wherein in each case one adjacent anodecurrent collector and cathode current collector is electricallyconnected by way of the connection element.
 19. A method formanufacturing a fuel cell system according to claim 1, wherein a firstand a second printed circuit board carrier is selected, each comprisingan upper side and a lower side, and on the upper side of both carriersthe steps of: depositing the metallisation onto the printed circuitboard carrier so that a printed circuit board arises, wherein metalfilms or thin sheets of a material selected from a group consisting ofcopper, nickel, gold, titanium or stainless steel and/or an alloythereof is laminated onto the printed circuit board material, or themetallisation is realised by way of coating and a subsequent galvanicreinforcement of the layer; selective etching-away or milling of themetallisation so that strip conductors arise which in a reaction regionform current collectors and connecting lugs, which border the currentcollectors in a smooth manner; incorporating gas distribution structuresinto the printed circuit board; depositing a diffusion layer; arecarried out and subsequently the membrane-electrode-assembly (MEA) isdeposited onto the upper side of the first printed circuit board, thefirst and the second printed circuit board with their upper sides facingone another are joined together and the connecting lugs are connected toone another in a perpendicular manner.
 20. A method according to claim19, wherein as a membrane electrode assembly (MEA) an MEA catalyticallycoated over its whole surface is selected and is segmented beforedeposition onto the first printed circuit board.
 21. A method accordingto claim 20, wherein the segmentation of the MEA is incorporated by wayof laser ablation and/or reactive ion etching.
 22. A method according toclaim 19, wherein after the incorporation of the gas distributionstructures, a raised part surrounding the reaction regions of the firstand second printed circuit board is deposited so that in each case arecess arises in the region of the reaction regions.